Trig question (1 Viewer)

[YBK]

I have to solve a trig equation and am getting stuck at the end...

solve: sin2x + 2cos^2x=0

So I replaced sin2x by 2sinxcosx

2sinx cosx + 2cos^2x=0
2cosx(sinx + cosx) = 0

Therefore

2cosx = 0
cosx = 0
x = 90, 270

sinx + cosx = 0
x= ??????????

if you can help me out, it'd be great.

Thanks!

 

[acmilan]

sinx + cosx = 0
sinx = -cosx

divide by cosx

tanx = -1

now solve

 

[YBK]

sinx + cosx = 0
sinx = -cosx

divide by cosx

tanx = -1

now solve

wow, thanks!!!!!!!!!!

it's all sooo clear now